Generally, ceramic-based honeycomb formed structures are produced through a procedure of, for example, forming (e.g., extruding) a raw material composition containing a predetermined ceramic source, a binder, and water to thereby form a formed structure of a honeycomb shape (a honeycomb formed structure) having a plurality of cells defined by partition walls, each cell serving as a fluid conduit; drying the honeycomb formed structure by means of hot air or an electromagnetic wave (high-frequency wave); and firing the dried honeycomb formed structure.
Ceramic honeycomb formed structures find uses such as cleaning of automobile exhaust gas and catalyst carriers. In recent years, cell partition walls of such honeycomb formed structures have come to be thinner, and partition walls and an outer wall of the aforementioned honeycomb formed structures are readily deformed or cracked during drying thereof. In order to prevent such deformation and cracking, drying is performed through high-frequency heating, which realizes drying of the entirety of the honeycomb formed structure more uniformly as compared with hot air drying. In the drying through high-frequency heating, an electromagnetic wave (high-frequency wave) having a frequency corresponding to water heating is applied to a honeycomb formed structure, thereby evaporating water by heating, whereby the honeycomb formed structure is dried. However, even when the high-frequency heating drying technique is employed, partial deformation of the dried honeycomb formed structure sometimes occurs in the production of the aforementioned ceramic honeycomb formed structure. For example, the problem occurs in the case in which, during drying of a honeycomb formed structure formed from a raw material composition, the formed honeycomb formed structure is placed on a stand; the honeycomb formed structure placed on the stand is transferred into a drying apparatus so as to dry the formed structure; the dried honeycomb formed structure is removed from the stand; and a newly formed undried honeycomb formed structure is placed on the stand so as to dry the undried honeycomb formed structure. In the above case, the stand is used repeatedly.
Meanwhile, in order to prevent deformation of partition walls and cracking of an outer wall, there has been proposed an approach in which high-frequency heating drying of a honeycomb formed structure is performed in a humidified atmosphere in a drying apparatus, thereby controlling the drying state of the honeycomb formed structure (see, for example, Patent Document 1). When this approach is employed, water may remain on a conveying tray on which a honeycomb formed structure is placed, since the atmosphere of the drying apparatus is highly humidified. Thus, there has been proposed a technique in which a conveying tray made of a predetermined porous ceramic material is employed so as to remove water. However, even when the technique is employed, if the conveying tray is used repeatedly, partial deformation and other defects of partition walls of the honeycomb formed structure are difficult to prevent.
[Patent Document 1]
Japanese Patent Application Laid-Open (kokai) No. 2002-283329